The present invention relates to a forklift having a transverse travel system that can be switched for transverse travel.
Vehicles having a transverse travel system have heretofore been found in large-sized transport vehicles and some types of loaders, and in forklifts they can be found in reach type electric vehicles. There are side forklifts for handling long-sized load, wherein the mast and forks are attached transversely of the direction of travel of the vehicle. In the engine type forklift of the counter type, however, there is no forklift that is capable of transverse travel in addition to doing ordinary work and that has the same functions as in the side forks. To establish such forklift, steering must be such that the front wheels (driving wheels) and the rear wheels (direction-change wheels) are directed exactly sideways. On this occasion, both front wheels are independently turned for direction change by actuators such as cylinders.
In the conventional forklift, however, in the case of changing the direction of the rear wheels to direct them exactly sideways, it has been difficult to attain compatibility between the direction change by the steering wheel during the ordinary travel and the direction change to transverse direction during the transverse travel. In addition, as methods for attaining compatibility between the direction change by the steering wheel during the ordinary travel and the direction change to transverse direction during the transverse travel, there is one in which a single rear wheel (steering axle) is used (3-wheel type). In this case, if the steering wheel is turned to the locked state during the transverse travel, transverse travel is allowed with the rear wheel directed sideways, but on the other hand, the 3-wheel type is inferior in stability to the 4-wheel type.
Accordingly, a first object of the present invention is to provide a forklift having a transverse travel system, which, despite the 4-wheel type, is capable of direction change during the ordinary travel and during the transverse travel.
Further, a second object of the invention is to provide a forklift having a transverse travel system, in which control for switching from ordinary travel to transverse travel can be smoothly effected by the operation of a common transverse travel control valve.
And a third object of the invention is to provide a forklift having a transverse travel system, which, despite the 4-wheel type, is capable of direction change during the ordinary travel and during the transverse travel and which simplifies the rear wheel turning means.
To achieve said first object, a forklift having a transverse travel system of the present invention with the vehicle body provided with a pair of right and left front wheels and a pair of right and left rear wheels, is characterized in that said front and rear wheels are respectively adapted to be turnable for direction change by 90 degrees, said pair of right and left front wheels are respectively operatively connected to drive shafts of travel driving devices, said travel driving devices being adapted to be turnable around vertical axes with respect to the vehicle body and being provided with front wheel turning means, while said pair of right and left rear wheels are adapted to be turnable around vertical axes with respect to the vehicle body and are provided with rear wheel turning means, said rear wheel turning means having a direction change cylinder and a pair of right and left rear wheel transverse travel cylinders that are adapted to separately turn the rear wheels when the direction change cylinder is in the neutral position and also adapted to assume a predetermined inoperative position during the actuation of the direction change cylinder.
According to the above arrangement of the invention, during the ordinary travel, the right and left front wheels and right and left rear wheels are longitudinally directed. At the time of ordinary travel, the steering wheel is turned clockwise or counterclockwise and the direction change cylinder is actuated by an orbit roll, when both rear wheel transverse travel cylinders are in a predetermined inoperative position and perform the function of a link, so that the rear wheels can be turned for direction change and turned according to the operation of the steering wheel. Further, when the direction change cylinder is actuated to move to the limit, the right and left rear wheels can be turned for direction change into an inclined state with their rear ends approaching each other, thereby making it possible to make a pivot turn.
In switching from ordinary travel to transverse travel, for example, a lever type transverse travel mode switch is operated to actuate the front wheel turning device and rear wheel turning device. That is, the front wheel turning device is actuated to turn the front wheels around vertical axes for direction change by 90 degrees (directed exactly sideways) with respect to the vehicle body. In this case, since the front wheels are integral with the travel driving device, such 90-degree direction change with respect to the vehicle body can be easily and smoothly effected.
Further, the rear wheel turning device is actuated to turn the rear wheels around vertical axes for direction change by 90 degrees (directed exactly sideways) with respect to the vehicle body. On this occasion, in the rear wheel turning device, with the direction change cylinder put in the neutral (linear movement) position, the rear wheel transverse travel cylinders are actuated, whereby the 90-degree turn of the rear wheels can be easily and smoothly effected.
After the front wheels and rear wheels have thus been turned for direction change so that they are directed exactly sideways, the front wheels are driven forward and backward by the travel driving device, whereby the forklift can be transversely moved to the right or left. On this occasion, the pair of right and left rear wheels are rotated in a follow-up manner. Thus, according to the invention, despite the 4-wheel type, direction change during the ordinary travel and during the transverse travel can be reliably made without requiring complicated electric control.
In order to achieve the second object, in a first embodiment of the invention relating to a forklift having a transverse travel system, the forklift is characterized in that said front wheel turning means has a front wheel transverse travel cylinder, said front wheel transverse travel cylinder and said rear wheel transverse travel cylinder being connected in parallel to a common transverse travel control valve respectively through open/close valves, wherein the rear wheel open/close valve is opened in response to a transverse travel operation, the rear wheel transverse travel cylinder is actuated to move to the transverse travel side in response to the operation of the transverse travel control valve, and the completion of the transverse orientation of the rear wheels is detected, whereby the rear wheel open/close valve is closed and the front wheel open/close valve is opened.
According to this first embodiment, when the transverse travel mode switch is operated, first the rear wheel open/close valve alone is opened, so that it is possible to turn the rear wheels for direction change by 90 degrees with respect to the vehicle body by actuating the rear wheel transverse travel cylinders by the operation of the transverse travel control valve. And the completion of the turning of the rear wheels for direction change is detected to close the rear wheel open/close valve and open the front wheel open/close valve, so that it is possible to turn the front wheels for direction change by 90 degrees with respect to the vehicle body by actuating the front wheel transverse travel cylinder by the operation of the transverse travel control valve.
This makes the transverse travel mode possible, so that the forklift can be transversely moved to the right or left by driving the front wheels forward and backward through the travel driving device. When this transverse travel is in progress, the front wheel open/close valve is kept open, so that by suitably operating the transverse travel control valve, it is possible to move the front wheel transverse travel cylinder only in a designated range; thus, positioning, turning and correction can be made during the transverse travel.
Thus, according to the first embodiment, control of switching from ordinary travel to transverse travel can always be smoothly effected despite the simple and inexpensive arrangement that operates the common transverse travel control valve. And the subsequent operation of the transverse travel control valve enables smooth control of transverse travel.
In a second embodiment of the invention relating to a forklift having a transverse travel system, the forklift is characterized in that the rear wheel transverse travel cylinders of the rear wheel turning means are adapted to move the direction change cylinder, which is now in the neutral position, back and forth so as to turn the rear wheels for direction change by 90 degrees, and also adapted to assume a predetermined inoperative position during the actuation of the direction change cylinder.
According to this second embodiment, in switching from ordinary travel to transverse travel, with the direction change cylinder put in the neutral position, for example, a lever type transverse travel mode switch is operated to actuate the front wheel turning means and rear wheel turning means. That is, the front wheel turning means is actuated to turn the front wheels around vertical axes for direction change by 90 degrees (directed exactly sideways) with respect to the vehicle body. Further, the rear wheel turning means is actuated to turn the rear wheels around vertical axes for direction change by 90 degrees (directed exactly sideways) with respect to the vehicle body. On this occasion, in the rear wheel turning means, with the direction change cylinder put in the neutral (linear movement) position, the rear wheel transverse travel cylinders are actuated, whereby turning of the rear wheels for direction change can be easily and smoothly effected.
After the front wheels and rear wheels have thus been turned for direction change so that they are directed exactly sideways, the front wheels are driven forward and backward, so that the forklift can be transversely moved to the right or left. Thus, according to this second embodiment, despite the 4-wheel type, the turning for direction change during the ordinary travel and the turning of the direction change wheels to direct the latter exactly sideways during the transverse travel can be reliably effected without requiring complicated electric control.
In a third embodiment of the invention relating to a forklift having a transverse travel system, the forklift is characterized in that the rear wheel turning means respectively have direction change cylinders corresponding to both rear wheels, at least one of said direction change cylinders being electrically controlled.
According to this third embodiment, despite the 4-wheel type, turning for direction change during normal travel can be reliably effected and so can be transverse travel. And in the rear wheel turning means, at least one of the two direction change cylinders is electrically controlled, so that turning of both rear wheels for direction change can always be smoothly effected without a time lag.
In order to achieve the third object, in a fourth embodiment of the invention relating to a forklift having a transverse travel system, the forklift is characterized in that the rear wheel turning means has a direction change cylinder and a pair of right and left rear wheel transverse travel cylinders, said cylinders having integrated main bodies, said direction change cylinder having its piston rod fixed to the vehicle body and its main body adapted to be movable, said rear wheel transverse travel cylinders being adapted to separately turn the rear wheels when the direction change cylinder is in the neutral position and also adapted to assume a predetermined inoperative position during the actuation of the direction change cylinder.
According to this fourth embodiment, the rear wheel turning means is actuated to turn the rear wheels around vertical axes for direction change by 90 degrees (directed exactly sideways) with respect to the vehicle body. On this occasion, in the rear wheel turning means, with the direction change cylinder put in the neutral (linear movement) position, the rear wheel transverse travel cylinders are actuated, so that the turning of the rear wheels for direction change by 90 degrees can be easily and smoothly effected. Therefore, according to the fourth embodiment, despite the 4-wheel type, turning for direction change during the ordinary travel and during transverse travel can be reliably effected without requiring complicated electric control. Furthermore, the rear wheel turning means is constructed such that the main bodies of the direction change cylinder and rear wheel transverse travel cylinders are integrated and the direction change cylinder has its piston rod fixed to the vehicle body and its main body adapted to be movable; therefore, the whole structure can be simplified, and the movement of the direction change cylinder can be accurately reflected on the rear wheel transverse travel cylinders to improve relative positional accuracy.